Paris: Thirteen suspected Islamists have been charged in France with "criminal conspiracy connected to a terrorist enterprise" and illegal possession and transportation of weapons, officials said on Wednesday.

The thirteen, some of whom are members of a suspected extremist group called Forsane Alizza that was banned this year, were arrested on Friday in the wake of attacks by an Islamist gunman who killed seven people.

Nine of the suspects, including Forsane Alizza leader Mohamed Achamlane, were ordered to be remanded in custody as police investigate their alleged crimes which include a plan to kidnap a judge, officials said.

The charges against this batch of suspects came after French police swooped on more suspected radical Islamists in pre-dawn raids for the second time in less than a week on Wednesday, arresting 10 people.

The latest raids were carried out in the southern port city of Marseille as well as Roubaix near the Belgian border, and in several other locations in the country's south and southwest.

French authorities have vowed a crackdown on Islamist extremists after self-confessed al-Qaeda follower Mohamed Merah was killed in a police siege after shooting dead seven people, including three Jewish children.

The killings shocked France and came just weeks before the presidential election, with security becoming a major campaign theme and President Nicolas Sarkozy closing the gap in opinion polls on Socialist Francois Hollande.

But the French opposition has criticised the presence of television news cameras during the police raids as the images could be seen to bolster the chances of right-wing Sarkozy's re-election after the two-round poll.

Centrist candidate Francois Bayrou said it was normal for the state to round up people suspected of crimes but that when "that is done with journalists summoned and in the presence of cameras, I find that astonishing."